As an exemplary conventional art, a collision determination system in a “Vehicle Hood Actuating System” of Japanese Patent Laid-Open Publication No. 2001-80545 is cited. FIG. 11 is an overall view showing the vehicle hood actuating system having the collision determination system. In the vehicle hood actuating system, the collision determination system consists of a speed sensor 501 for detecting the vehicle speed, an acceleration sensor 503 for detecting an acceleration acting on a bumper 502 upon a collision of a vehicle 500 with an object of protection M, a deformation rate calculator 504 for calculating a bumper deformation rate from the information of acceleration detected by the acceleration sensor 503, a smoothing processor 505, a speed-threshold map 506 for varying the threshold of the bumper deformation rate in accordance with the vehicle speed, a hood actuating device including actuators 508 for holding up the proximal ends of a hood 509 by a predetermined amount, and an electric control unit (ECU) 507 for controlling the operation of the actuators 508. When a vehicle speed detected by the speed sensor 501 is a predetermined vehicle speed and a calculated bumper deformation rate exceeds the threshold, the control unit 507 determines that the collision object is a predetermined object of protection M and operates the actuators 508 to lift the hood 509 at their proximal ends. The hood actuating device lifts the hood 509, thereby mitigating the impact of a secondary collision of the protection object M with the hood 509.
In the above-described collision determination system, if a malfunction occurs in an acceleration sensing element, electric circuit or the like in the acceleration sensor 503, an invalid signal (acceleration signal of a great acceleration as provided upon the occurrence of collision) due to the malfunction may be supplied from the acceleration sensor 503 though in a no-collision state. Misidentifying the invalid signal as a normal valid signal, the control unit 507 may determine that a collision occurs and actuate the hood 509.
Air bag systems have employed a collision determination system having an impact sensor for sensing an impact of above a certain level provided in a control unit, which system being configured not to actuate air bags when the impact sensor detects nothing, even if a collision determination signal is supplied from the control unit. The impact sensor, however, is provided in the control unit and can only sense an impact sufficiently large to actuate air bags.
In a collision with an object of as small a weight as a pedestrian as a protection object of a collision determination system of the present invention, impact occurs only near a bumper as a colliding area. The impact sensor provided in the control unit as described above cannot sense a collision with an object of as small a weight as a pedestrian.
It might be possible to mount the control unit at the front end of a vehicle. It is, however, difficult to place the control unit in such a narrow space as a vehicle front end portion. Therefore the above-described impact determination system for use in air bag systems cannot be used for a collision determination system for actuating hood actuators, which is the subject matter of the present invention.
Thus desired is a collision determination system having a control unit which reliably determines whether a vehicle collides with an object and outputs an actuating signal as appropriate, even when an invalid signal due to a malfunction in an acceleration sensing element, electrical circuit or the like in an acceleration sensor is supplied.